US3887815A

US3887815A - Photoelectric smoke detector

Info

Publication number: US3887815A
Application number: US423530A
Authority: US
Inventors: Mamoru Kawakami
Original assignee: Hochiki Corp
Current assignee: Hochiki Corp
Priority date: 1972-12-14
Filing date: 1973-12-10
Publication date: 1975-06-03
Anticipated expiration: 1992-06-03
Also published as: GB1417790A; JPS4996891U; DE2361403A1; DE2361403C3; CH563630A5; DE2361403B2; FR2211128A5; JPS5545506Y2

Abstract

A photoelectric smoke detector comprising a source of light intermittently energized to flash by the output of a first oscillator, and a light receiving circuit energized and operated intermittently by the output of a second oscillator, wherein the oscillation periods of the first and second oscillators are different from each other, and the outputs of the first and second oscillators are applied to the light source through an AND gate, whereby the light receiving circuit is brought into operation when a light is emitted from the light source.

Description

United States Patent 191 Kawakami PHOTOELECTRIC SMOKE DETECTOR [75] Inventor: Mamoru Kawakami,Takatsuki,

Japan [73] Assignee: Hochiki Kabushiki Kaisha, Tokyo,

Japan [22] Filed: Dec. 10, 1973 [21] Appl. No.: 423,530

[30] Foreign Application Priority Data June 3, 1975 11/1972 Koning 250/209 X 4/1974 Bossons 250/214 R Primary Examiner-Walter Stolwein Attorney, Agent, or FirmWaters, Schwartz & Nissen [57] ABSTRACT A photoelectric smoke detector comprising a source of light intermittently energized to flash by the output of a first oscillator, and a light receiving circuit energized and operated intermittently by the output of a second oscillator, wherein the oscillation periods of the first and second oscillators are different from each other, and the outputs of the first and second oscillators are applied to the light source through an AND gate, whereby the light receiving circuit is brought into operation when a light is emitted from the light source.

[56] References Cited UNITED STATES PATENTS 3 Claims, 4 Drawing Figures 3,655,289 4/1972 Walker 250/206 X 1' 1 i r l i 1 OSCILLATOR P-q PULSE AMPLIFIER LIGHT souncs I OSClLLATOR PULSE AMPLlFlER 5 AMPLIFIER ALARM SIGNAL CIRCUIT LIGHT RECEIVER /4 I L'TI IIIur-m I975 3.887.815 SHEET I FIG. I PRIOR ART I S oscILLAToR PuLsE AMPLIFIER LIGHT souRcE I I I ALARM SIGNAL cIRcuIT AMPLIFIER LIGHT REcEIvER oscILLAToR PuLsE AMPLIFIER FIG. 2

1 I I I I oscILLAToR PULSE AMPLIFIER LIGHT souRcE I I 1 oscILLAToR PuLsE AMPLIFIER LIGHT REcEIvER f4 5 I AMPLIFIER I ALARM sIGHAL cIRcuIT PHOTOELECTRIC SMOKE DETECTOR FIELD OF THE INVENTION This invention relates to photoelectric smoke detectors.

BACKGROUND OF THE INVENTION Photoelectric smoke detectors are known in the art in which in order to realize a reduced power consumption, a light source operating circuit and a light receiving circuit are periodically energized in synchronism with each other so that the light source is intermittently operated and the light receiving circuit receives the flashes of light scattered by smoke. A disadvantage of this type of detector is that it is technically difficult to achieve the required synchronization of the light source operating circuit and the light receiving circuit due to the fact that the time constants of the component elements of the one circuit are not the same as those of the component elements of the other circuit and moreover a considerable time is required for pro viding the required synchronization both in the designing and manufacture of such detector.

In an attempt to overcome the foregoing difficulty, a photoelectric smoke detector has been proposed in Japanese Patent Application No. 80l39/l97l, in which the light source and the light receiving circuit are intermittently energized by the outputs of their own oscillators, and oscillation periods of the two oscillators are selected to differ from each other, whereby each time the light source andd the light receiving circuit come into operation simultaneously after a given number of cycles, detection of the presence of smoke is effected.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an intermittent energization type photoelectric smoke detector which eliminates the need for synchronized operation of the oscillators, insures simplified designing and adjustments and reduces the amount of power consumption still further.

In accordance with the present invention, there is thus provided a photoelectric smoke detector comprising a light source intermittently energized by the output of a first oscillator, a light receiving circuit adapted to rereceive light from the light source and energized by the output of a second oscillator to operate intermittently, the oscillation period of the first oscillator being different from that of the second oscillator, and an AND gate circuit connected between the first oscillator and the light source and controlled by the outputs of the first and second oscillators, whereby the light source is operated only when the outputs of the first and second oscillators operating with the different oscillation periods appear simultaneously, thereby to eliminate any wasteful operation of the light source and thus to reduce the amount of power consumption still further.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a block diagram of a prior art photoelectric smoke detector;

FIG. 3 is a pulse waveform diagram useful for explaining the operation of the device shown in FIG. 1;

FIG. 2 is a block diagram showing an embodiment of a photoelectric smoke detector according to the present invention; and

FIG. 4 is a pulse waveform diagram useful for explaining the operation of the embodiment shown in FIG. 2.

DETAILED DESCRIPTION FIG. I of the accompanying drawing is a block diagram showing the general construction of the photoelectric smoke detector disclosed in Japanese Patent Application No. l39/l97 I. In this device, the output oscillations or rectangular pulses from an oscillator I are amplified by a pulse amplifier 2 and, a light source or lamp 3 is energized by the amplified output of the amplifier 2. The light source 3 then flashes so that when the flashes of light from the light source 3 are scattered by smoke, part of the scattered flashes of light is received by a light receiver 4 which in turn detects the presence of the smoke. The output of the light receiver 4 is applied, after amplification by an amplifier 5, to an alarm signal circuit 6 to give an alarm. In this case, the light receiver and the amplifier do not operate at all times, but they are energized and operated intermittently by the rectangular pulses generated by an oscillator 8 and then amplified by an amplifier 7. The alarm signal generating operation of this device will be described further with reference to FIG. 3.

Referring to FIG. 3, numeral 11 designates the waveform of the pulse voltage for energizing the light source 3, and numeral 12 designates the waveform of the pulse voltage for energizing and operating the light receiver 4 and the amplifier 5. At times l r r r, and r,,,, the flashing operation of the light source 3 and the operation of the light receiver 4 and its associated circuits coincide with each other thus permitting the performance of smoke detecting operations. At other times, either the light source 3 or the light receiver 4 or both of them are inoperative and hence no smoke detecting operation is performed. Of course, the repetition frequencies of these pulses are selected to be large and therefore the performance of the smoke detecting operation at the times r I I,, r I and r means that the occurrence of smoke can be almost simultaneously detected and that the operation of this device as a smoke detector is satisfactory. However, at times t t and so on the light source 3 is operated wastefully. Therefore, while this prior art device has the advantages of the considerably reduced power consumption and simplified designing and adjustment due to the fact that there is no need to synchronize the two oscillators, there still exists room for further reduction of power consumption since the light source and the light receiver are separately operated wastefully excepting at those times when both of them come into operation simultaneously. Since the amount of power consumed by this type of light source is generally considerably large, it is possible to realize a further reduction in the power consumption of the whole device by eliminating such wasteful operation of the light source.

Referring now more specifically to FIG. 2 of the drawings, there is illustrated a block diagram of a photoelectric smoke detector which embodies the present invention and which overcomes the foregoing deficiencies of the prior art devices. In FIG. 2, the same reference numerals are employed for the component parts which are similar to those used in the device of FIG. I. Numeral 9 designates an AND gate circuit which receives as its inputs the outputs of

pulse amplifiers

2 and 7. Symbols A and B designate respectively a light source operating circuit and a light receiving circuit of the smoke detector. The light source operating circuit A comprises the first oscillator 1, pulse amplifier 2 for amplifying the output of the first oscillator l. and light source 3 intermittently operated by the output of the pulse amplifier 2 and comprising for example a light emitting diode or lamp. The light receiving circuit B comprises the light receiver 4 having a photoelectric conversion element such as a photoelectric cell or photo transistor to receive the flashes of light emitted from the light source 3 and scattered by smoke. amplitier 5 for amplifying the output of the light receiver 4, alarm signal circuit 6 responsive to the output of the amplifier 5 to generate a detected smoke signal, and the second oscillator 8 and amplifier 7 for periodically and intermittently energizing the component parts 4 through 6. The oscillation periods of the first and second oscillators l and 2 are selected to differ from each other and each of them comprises for example a blocking oscillator or astable multivibrator. For instance, as shown in FIG. 4. the oscillator l generates pulse output ll having an on-time 1 and an off-time tr 4 1,,..). and the oscillator 8 generates pulse output 12 having an on-time T and an off-time T (T,,,, T z 6.5 t

The operation of the embodiment shown in FIG. 2 will be described with reference to FIG. 4. The oscillators l and 8 oscillate independently of each other at different frequencies so that the oscillaor l generates pulses 11 having a narrower time width and the oscillator 8 generates pulses l2 having a wider time width. These pulses 11 and 12 are respectively amplified by the

amplifiers

2 and 7 after which the pulses 12 are directly applied to the light receiver 4 and the amplifier to operate them for a length oftime corresponding to the time width of each pulse 12. On the other hand. the light source 3 receives the outputs of the oscillators l and 8 through the AND gate circuit 9 so that the light source 3 flashes only at times l i t I, and r Since the light receiving section is invariably in operation at these times. the smoke detecting operation is invariably carried out each time the light source 3 flashes. In the case of the prior art device, as indicated by dotted lines. the light source 3 flashes at times I I... and so on when the light receiving section is inoperative and therefore these flashes are all wasted. The device according to the present invention eliminates such wasteful flashes of the light source. thereby ensuring a longer life of the light source and a further decrease in the power consumption.

It will thus be seen from the foregoing description that the device according to the present invention not only eliminates the need to synchronize the effective operating times of the light source operating circuit and the light receiving circuit with the resultant elimination of the required labor and special parts for the adjustment therefor. but also minimizes the amount of power consumption due to the absence of any wasteful operation of the light source.

What we claim:

1. A photoelectric smoke detector comprising a source of light, a first oscillator connected to said source, said source being adapted for being intermittently energized by the output of said first oscillator, in second oscillator. a light receiving circuit including a photoelectric means adapted for being energized by the output of a second oscillator thereby to come into operation intermittently for receiving light scattered by smoke generated by the source of light. the first and second oscillators having different oscillation periods, and an AND gate circuit controlled by the outputs of the first and second oscillators being connected between the first oscillator and the source of light.

2. A photoelectric smoke detector according to claim 1. wherein the oscillation period of the first oscillator is shorter than the oscillation period of the second oscillator.

3. A photoelectric smoke detector according to claim 1. wherein the pulse width of the second oscillator is wider than the pulse width of the first oscillator.

Claims

1. A photoelectric smoke detector comprising a source of light, a first oscillator connected to said source, said source being adapted for being intermittently energized by the output of said first oscillator, a second oscillator, a light receiving circuit including a photoelectric means adapted for being energized by the output of a second oscillator thereby to come into operation intermittently for receiving light scattered by smoke generated by the source of light, the first and second oscillators having different oscillation periods, and an AND gate circuit controlled by the outputs of the first and second oscillators being connected between the first oscillator and the source of light.

2. A photoelectric smoke detector according to claim 1, wherein the oscillation period of the first oscIllator is shorter than the oscillation period of the second oscillator.